The present invention relates to a method and apparatus for assembling electric motors and in particular includes a provision for preloading the bearings of the electric motor during assembly.
Electric motors are generally manufactured in two major parts. A rotary hub assembly houses permanent magnet members and encloses a stator assembly which includes stator coils surrounding an electromagnet. The hub assembly is joined to the stator assembly which includes a rotor shaft through upper and lower bearings. The stator assembly shaft is joined to both upper and lower bearings along the inner race of each while the hub is affixed to the outer race of both the upper and lower bearings. When the coils of the stator are energized, the hub assembly and its permanent magnet members will rotate about the shaft.
A particular problem that is encountered in the use of such bearings is that, depending upon how the motor is assembled, the coupling between the rotary hub assembly and the stator assembly can be either too loose or too tight. If the bearings are too loose there is too much play in the hub assembly, and in tightly constructed configurations the hub assembly may actually be impeded in its attempt to rotate properly. On the other hand, if the bearings are too stiff there can be too much friction between the hub assembly and the stator, and the motor will not provide the necessary torque for the particular application.
Heretofore, the bearing stiffness that resulted from the way in which the hub and stator were joined together was largely a matter of chance because there was no attempt made to control the bearing stiffness during assembly. Whether the bearings were preloaded in any way was determined by the orientation of the parts when the glue joining the parts together set. This haphazard approach to motor assembly caused many motors to fail.